Manufacturing of camshafts often results in small undulations along cam lobe surfaces commonly referred to as chatter. During engine operation, valve lifter mechanisms roll and/or slide along the cam lobe surface encountering the surface undulations. Undulations having a certain amplitude and frequency may create objectionable levels of audible noise when the valve lifter mechanisms encounter the cam lobe surface. Therefore, a boundary between acceptable and unacceptable levels of noise due to the undulations is desired.
In one method to define the boundary, a maximum amplitude of the undulations is specified using piecewise threshold values within discrete frequency ranges. More specifically, multiple bins are created with discrete frequency bandwidths. The amplitude of the bins define the boundary between acceptable and unacceptable noise levels. However, experimental evidence suggests that the boundary between acceptable and unacceptable noise levels is not a discrete function. Therefore, the amplitude of the bin may be above or below the boundary for a portion of the bandwidth of the bin. Thus, some cam lobes with acceptable undulations may be rejected while some cam lobes with unacceptable undulations may be used.